Carrier-supported catalyst and process for making mono-carboxylic anhydrides

ABSTRACT

Monocarboxylic anhydrides of the general formula (RCO) 2  O are made by reacting a carboxylic acid ester or dialkylether of the general formulae RCOOR and ROR, respectively, in which R stands for one and the same alkyl radical having from 1-4 carbon atoms, with carbon monoxide in gas phase, in the presence of iodine or bromine or their compounds as a reaction promoter and also in the presence of a carrier-supported catalyst containing noble metal compounds of group VIII of the Periodic System, at temperatures of 130°-400° C. and under pressures of 1-150 bars. To this end, a novel carrier-supported catalyst is used in which the carrier material has a noble metal/chelate-compound formed of the noble metal compound and a chelator containing organonitrogen, organophosphorus, organoarsenic or organosulfur groups applied to it.

This invention relates to a process for making monocarboxylic anhydridesof the general formula (RCO)₂ O by reacting a carboxylic acid ester ordialkylether of the following general formulae RCOOR and ROR,respectively, in which R stands for one and the same alkyl group havingfrom 1-4 carbon atoms, with carbon monoxide in gas phase, in thepresence of iodine or bromine or their compounds as a reaction promoterand also in the presence of a carrier-supported catalyst containing anoble metal compound selected from group VIII of the Periodic System ofthe elements, at temperatures of 130°-400° C. and under pressures of1-150 bars.

Processes of this kind which are carried out in gas phase with the useof a carrier-supported catalyst have already been described in GermanSpecification DE-A No. 24 50 965 and in Japanese Specification No.47921/1975. These processes avoid the difficulties normally accompanyingoperations in liquid phase, e.g. the difficult separation and recycle ofsuspended and partially dissolved catalyst and, under circumstances,promoter.

The two Specifications describe gas phase processes wherein solidcarrier-supported catalysts made by impregnating the carrier materialwith a dissolved or suspended and even with complex noble metalcompounds are used. In this way, it is not possible to fix e.g. anorganonitrogen or organophosphorus compound containing trivalentnitrogen or phosphorus in the carrier-supported catalyst; this howeverhas been found generally to affect the catalyst performance and reactionselectivity.

The present invention avoids this deficiency and to this end providesfor the catalyst carrier to be impregnated with a noblemetal/chelate-compound which has one or more promoters selected fromprincipal group V, e.g. an organylamine or phosphine, already integratedin it.

The invention comprises more particularly using

(1) a carrier-supported catalyst in which the carrier has a noblemetal/chelate-compound formed of the noble metal compound and a chelatorcontaining organonitrogen, organophosphorus, organoarsenic ororganosulfur groups applied to it.

Further preferred and optional features of the invention provide:

(2) for the carrier of the carrier-supported catalyst to have a nonnoble metal/chelate-compound formed of a non noble metal compoundselected from the 6th or 8th subgroup of the Periodic System of theelements and a chelator containing organonitrogen, organophosphorus,organoarsenic or organosulfur groups additionally applied to it;

(3) for the carrier-supported catalyst to contain a non noble metalcompound selected from the 1st through 3rd principal groups or the 4ththrough 6th or 8th subgroups of the Periodic System of the elements asan additional promoter;

(4) for the carrier in the carrier-supported catalyst to have a chelatecompound and one of the following chelators:

(a) Y--(CH₂)_(n) --Y

(b) Y--CH═CH--Y

(c) φ₂ P--CH═CH--Pφ₂

(d) φ₂ As--CH═CH--Asφ₂

(e) φ₂ P--CH₂ --CH₂ --Pφ--CH₂ --CH₂ --Pφ--CH₂ --CH₂ --Pφ₂

(f) φ₂ P--CH₂ --CH₂ --Pφ--CH₂ --CH₂ --Pφ₂ ##STR1## (h) P(--CH₂ CH₂--Pφ₂)₃ (i) R¹ --C[--(CH₂)_(n) --Y]₃ ##STR2## in which φ stands for C₆H₅ --;

Y stands for --Nr₂ ², an aryl group containing nitrogen, --PR₂ ², --AsR₂², --SR² or --SH;

R¹ stands for --H, a C₁ -C₅ -alkyl or --C₆ H₅ ;

R² stands for a C₁ -C₆ -alkyl, a C₅ -C₈ -cycloalkyl or --C₆ H₅ or C₆ H₅CH₂ --;

n stands for 1 through 6, preferably 1-4;

m stands for 0 through 8, preferably 0-3, and

x stands for 1 or 2 applied to it;

(5) for the carrier-supported catalyst to contain an inorganic oxidiccarrier or an active carbon carrier.

(6) for the carrier-supported catalyst to contain altogether 0.01-50 wgt%, preferably 0.1-20 wgt %, chelate compound and non noble metalcompound, if desired;

(7) for the carrier-supported catalyst to be used in the form ofparticles having a size of 1 through 20 mm.

The invention also relates to the catalyst itself which is used formaking monocarboxylic anhydrides by subjecting a suitable ester or etherto a carbonylation reaction and which is characterized in that thecarrier has a noble metal/chelate-compound formed of a noble metalbelonging to the 8th subgroup of the Periodic System of the elements anda chelator containing organonitrogen, organophosphorus, organoarsenic ororganosulfur groups applied to it.

Further preferred and optional features of the carrier-supportedcatalyst of this invention provide:

(1) for the carrier to have a non noble metal/chelate-compound formed ofa non noble metal selected from the 6th or 8th subgroup of the PeriodicSystem of the elements and a chelator containing organonitrogen,organophosphorus, organoarsenic or organosulfur groups additionallyapplied to it;

(2) for the carrier-supported catalyst to contain a non noble metalcompound selected from the 1st through 3rd principal groups or the 4ththrough 6th or 8th subgroups of the Periodic System of the elements asan additional promoter;

(3) for the carrier to have a chelate compound formed of a metalcompound and one of the chelators identified under item (4), (a) through(k) hereinabove applied to it;

(4) for the carrier-supported catalyst to contain an inorganic oxidiccarrier or active carbon;

(5) for the carrier-supported catalyst to contain altogether 0.01-50 wgt%, preferably 0.1-20 wgt %, chelate compound and non noble metalcompound, if desired.

The catalyst carriers which should preferably be used comprisesinorganic oxides, e.g. SiO₂, Al₂ O₃, MgO, TiO₂, La₂ O₃, ZrO₂, zeolite,clay, NiO, Cr₂ O₃, WO₃ or corresponding mixed oxides, but also activecarbon having a BET-surface area of 1-1000 m² /g, preferably 30-400 m²/g.

The promoters of the 5th or 6th principal group are chemically combinedin the chelators used and constitute themselves one of their functionalgroups encasing the noble metal compounds selected from group VIII,especially Rh, Ir, Pd, or Ru, and also the non noble metal compounds, ifany, selected from the 6th or 8th subgroup, especially Cr or Ni, butalso W, Fe and Co, like pincers of a cray-fish.

One of the advantages of the carrier-supported catalyst and process ofthis invention resides in the fact that the promoters necessary forincreasing the catalyst performance and selectivity and selected fromprincipal group V or VI of the Periodic System of the elements form afunctional group Y in the chelators and thus are fixed. It is thereforeunnecessary, e.g. for an organonitrogen or organophosphorus promoter tobe separated and recycled. The present process for making monocarboxylicanhydrides compares favorably in its higher catalyst performance andselectivity with the prior art methods described hereinabove, which arealso carried out in gas phase and with the use of a carrier-supportedcatalyst.

A further advantage of ths invention is seen to reside in the fact thatthe noble metal/chelate-compounds and optionally non noblemetal/chelate-compounds applied to the carrier fail to commence meltingat the reaction temperatures necessary for making monocarboxylicanhydrides.

The carrier-supported catalyst and process of this invention are moreparticularly used for making acetic anhydride from methyl acetate ordimethylether in the presence of methyl iodide or methyl bromide as areaction promoter. Further suitable promoters are HI, HBr or moregenerally RI or RBr, where R stands for an alkyl group having 1-4 carbonatoms.

The useful carrier materials have already been specified hereinabove;useful mixed oxides are, e.g. Cr₂ O₃ --Al₂ O₃, WO₃ --Al₂ O₃, MgO--Al₂O₃, SiO₂ --Al₂ O₃ or ZrO₂ --Al₂ O₃. The carrier-supported catalystshould preferably contain 0.01-5 wgt % noble metal and present aparticle size of 1 to 20 mm.

The noble metal compounds which should conveniently be used for makingthe present carrier-supported catalyst, comprise e.g. the followingcompounds

Rhodium:

RhCl₃, RhCl₃.3H₂ O, RhBr₃, RhI₃, Rh(NO₃)₃, Rh₂ (CO)₄ Cl₂, Rh₂ (CO)₄ Br₂,Rh(CO)₄ I₂, [P(C₆ H₅)₃ ]₃ RhCl, [P(C₆ H₅)₃ ]₂ Rh(CO)Cl, Rh₆ (CO)₁₆, Rh₄(CO)₁₂, Rh₂ (O₂ CCH₃)₄, [RhCl(C₈ H₁₂)]₂ ;

Iridium:

IrCl₃, [Ir(CO)₃ Cl]₂, Ir[P(C₆ H₅)₃ ]₂ (CO)Cl, Ir₄ (CO)₁₂, [IrCl(C₈H₁₂)]₂, Cl(CO)₂ Irpyr (pyr=C₆ H₅ N);

Palladium:

PdCl₂, PdBr₂, PdI₂, (CH₃ CO₂)₂ Pd[P(C₆ H₅)₃ ]₂, PdCl₂ [P(C₆ H₅)₃ ]₂,Pd(O₂ CCH₃)₂, PdCl₂ (C₈ H₁₂), (C₆ H₅ CN)₂ PdCl₂ ;

Ruthenium:

RuCl₃, Ru₃ (CO)₁₂, RuCl₂ [P(C₆ H₅)₃ ]₃, RuCl₂ (CO)₂ [P(C₆ H₅)₃ ]₂,[RuCl₂ (CO)₃ ]₂.

Useful non noble metal compounds selected from the 6th or 8th subgroup,especially Cr, Ni, but also W, Fe, Co which also undergo reaction withthe chelator, comprise e.g. the following:

Chromium:

Cr(CO)₆, CrCl₃, C₇ H₈ Cr(CO)₃.

Nickel:

Ni(CO)₄, [P(C₆ H₅)₃ ]₂ Ni(CO)₂, NiCl₂, Ni(C₈ H₁₂)₂.

The non noble metal compounds selected from the 1st through 3rdprincipal groups or the 4th through 6th subgroups or 8th subgroup of thePeriodic System of the elements, preferably compounds of Li, Na, Mg, Ca,Al, Ti, Zr, V, Cr, W, Fe, Co, Ni are comprised, e.g. of hydroxides,carbonates, carbonyls, hydrides, halides and further salts. It ispossible for these non noble metal compounds to be additionally appliedto the catalyst carrier, e.g. in the form of a solution by impregnatingthe carrier therewith.

For making the carrier-supported catalyst of this invention, it isnecessary first to have the chelator with the functional groups Y, whichis a commercially available product or can be made by methods describedin literature. Speaking generally, the chelator is contacted with asolution of one of the noble metal compounds of group VIII and, ifdesired, one of the non noble metal compounds of the 6th or 8thsubgroups with the resultant formation, in known fashion, of chelatecompounds having melting points higher than the temperature commonlyemployed in a carbonylation reaction for making monocarboxylicanhydrides. Next, the carrier material is impregnated with the dissolvedconventional chelate compounds to give the finished catalyst. Thesolvents for the chelate compounds comprise polar and unpolar solvents,e.g. dichloromethane (methylene chloride), chloroform, methanol,benzene, toluene or xylene, in which the carrier material is suspended.Details are indicated in the catalyst description hereinafter.

The quantitative ratio of carboxylic acid ester or dialkylether andiodine(compound) or bromine(compound) in the reaction zone may varywithin wide limits. Generally, however, 1 to 500 mols, preferably 1 to100 mols, carboxylic acid ester and/or dialkylether is used per 1 moliodine (compound) or bromine(compound). The temperature selected for thereaction zone should be high enough to always have a gaseous reactionmixture therein, irrespective of the conversion rate, and preferably isbetween 150° and 250° C. The preferred pressure is between 5 and 30bars.

The reaction mixture should conveniently be contacted with the solidcarrier-supported catalyst over a period of from 1 to 1000 seconds,preferably 1 to 180 seconds. The conversion should suitably be effectedin a flow tube arranged in upright position, packed with thecarrier-supported catalyst or in an autoclave provided with a stirrer orin a shaking autoclave, having the carrier-supported catalyst placedtherein. While the carbonylation is generally effected under practicallyanhydrous conditions, it is allowable for it to be carried out in thepresence of minor amounts of water as they are normally found incommercially available starting materials, which however should notexceed 1 mol %, based on the starting materials. In addition, thecarbonylation remains substantially uneffected by the presence of minoramounts of methanol in the starting materials or of hydrogen incommercial carbon monoxide.

The reaction mixture coming from the carbonylation zone is gaseous andcontains carbon monoxide, methyl iodide, acetic anhydride, unreactedmethyl acetate or dimethylether and, under circumstances, minorproportions of acetic acid. The gaseous reaction mixture is cooled withcondensation of acetic anhydride, under circumstances, acetic acid.Uncondensed gases, such as CO, CH₃ I, methyl acetate or dimethyletherare recycled to the reaction zone, the reacted ester or ether and COportions being continuously renewed. The anhydrides are easy toseparate, i.e. in uncomplicated fashion, by cooling the effluentreaction mixture and recycling the uncondensed gas. This is a particularadvantage of the process of this invention. The carrier-supportedcatalyst is not contaminated; it remains in the reaction zone. As aresult, the entire process is rendered considerably simpler.

The following Examples illustrate the invention which is naturally notlimited thereto:

EXAMPLES

Autoclave test

A stainless steel (Hastelloy C) autoclave (capacity 0.25 l) providedwith a stirrer, various inlets and outlets and a turnable basketreceiving the catalyst was used. The carboxylic acid ester ordialkylether was reacted in gas phase with CO-gas in the presence of theagitated solid carrier-supported catalyst. The catalyst was placed inthe turnable catalyst basket which also permitted the gases to be mixed.The autoclave was charged with 2.5 ml of a liquid mixture of 20 volumeparts methyl iodide and 80 volume parts ester or ether, and heated tothe reaction temperature. The carbonylation was started by injectingcarbon monoxide. The CO-pressure was maintained constant by continuedinjection of gas. Details are indicated in the Examples.

EXAMPLE 1

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g)methyl iodide and 1.60 gcatalyst No. 1 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1 h,the catalyst performance was found to be 260 g Ac₂ O per g Rh per hour.The yield of Ac₂ O, based on the ester used, was 64% and the selectivity95%.

EXAMPLE 2

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.60 gcatalyst No. 1 were reacted in the autoclave with carbon monoxide at175° C. under a CO-pressure of 20 bars. After a reaction period of 1 h,the catalyst performance was found to be 220 g Ac₂ O per g Rh per hour.The yield of Ac₂ O, based on the ester used, was 54% and the selectivity96%.

EXAMPLE 3

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.77 gcatalyst No. 2 were reacted in the autoclave with carbon monoxide at166° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 280 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 64% and theselectivity 97%.

EXAMPLE 4

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.77 gcatalyst No. 2 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 380 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 86% and theselectivity 93%.

EXAMPLE 5

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.78 gcatalyst No. 3 were reacted in the autoclave with carbon monoxide at200° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 35 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 11.6% and theselectivity 87%.

EXAMPLE 6

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.70 gcatalyst No. 4 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 450 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 24% and theselectivity 94.7%.

EXAMPLE 7

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 4.4 gcatalyst No. 5 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was 150 g Ac₂ O per g Rh per hour. Theyield of Ac₂ O, based on the ester used, was 78% and the selectivity94%.

EXAMPLE 8

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.7 gcatalyst No. 6 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 190 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 45% and theselectivity 93%.

EXAMPLE 9

A steel tube 20 mm wide and 450 mm long was used as a flow tube inupright position and charged with 27.4 g catalyst No. 2 which howevercontained 0.4 wgt % Rh. 11 Nl CO (Nl=liter measured at 0° C. under 1.013bar) and an evaporated mixture (13 ml liquid) of methyl acetate andmethyl iodide (molar ratio 11:1) were passed through the flow tube at172° C. under a pressure of 12.5 bars.

The effluent reaction mixture was cooled to 0° C. at atmosphericpressure and analyzed gas-chromatographically. The space/time-yield wasfound to be 71 g Ac₂ O per liter per hour. The yield of Ac₂ O, based onthe ester used, was 30% and the selectivity 96%.

The carbonylation reaction was effected over a period of 100 hours underthese reaction conditions; the performance of the carrier-supportedcatalyst could not be found to have been reduced.

EXAMPLE 10

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.7 gcatalyst No. 7 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 300 g Ac₂ O per g Rhhour. The yield of Ac₂ O, based on the ester used, was 62% and theselectivity 95%.

EXAMPLE 11

1.86 g dimethylether, 0.5 ml (1.14 g) methyl iodide and 1.7 g catalystNo. 7 were reacted in the autoclave with carbon monoxide at 180° C.under a CO-pressure of 20 bars. After a reaction period of 1 hour, thecatalyst performance was found to be 100 g Ac₂ O per g Rh per hour. Theyield of Ac₂ O, based on the ether used, was 20.6% and the selectivity85%.

EXAMPLE 12

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.7 gcatalyst No. 8 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 243 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 50.1% and theselectivity 94%.

EXAMPLE 13

2 ml (1.86 g) methyl acetate, 0.5 ml (1.14 g) methyl iodide and 1.7 gcatalyst No. 9 were reacted in the autoclave with carbon monoxide at180° C. under a CO-pressure of 20 bars. After a reaction period of 1hour, the catalyst performance was found to be 250 g Ac₂ O per g Rh perhour. The yield of Ac₂ O, based on the ester used, was 55.0% and theselectivity 95.5%.

Description of catalyst preparation

In each particular case, the catalyst carrier was activated by drying itover a period of 10 hours at 200° C. under a pressure of about 0.133millibar. All syntheses were run in the presence of nitrogen withexclusion of oxygen and water, and all reagents were previously driedusing molecular sieve 4 A.

The following abbreviations are used hereinafter

φ=C₆ H₅ --

dpe=φ₂ P--CH₂ CH₂ --Pφ₂ ; dpen=φ₂ P--CH═CH--Pφ₂

dpb=φ₂ P--(CH₂)₄ --Pφ₂

Tetraphos-1=φ₂ PCH₂ CH₂ PφCH₂ CH₂ PφCH₂ CH₂ Pφ₂

Catalyst No. 1

Al₂ O₃ ] [Rh(dpe)₂ ]⁺ Cl⁻

3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameter of3 mm, an inner BET-surface area of 125 m² /g a pore volume of 0.9 ml/gwere added to 150 mg (16 mg Rh) compound of the formula [Rh(dpe)₂ ]Cl(melting point=217° C.; prepared from 1,2-bis-(diphenylphosphine)ethaneand dichlorotetracarbonyldirhodium, cf. A. Sacco et al., J. Chem. Soc.(London), (1964), 3274; for prepartion of [Rh(CO)₂ Cl]₂ from RhCl₃.3H₂ Oand CO-gas, see J. A. McCleverty et al., Inorg. Synth. 8 (1966), page211; for preparation of φ₂ PCH₂ CH₂ Pφ₂, see W. Hewertson et al., J.Chem. Soc. (London), (1962), 1490) dissolved in 100 ml dichloromethane,under N₂.

The yellow suspension was heated to boiling while stirring and refluxedover a period of 12 hours after which the dichloromethane was found tohave been completely decolorized. Next, the dichloromethane was removedunder reduced pressure and the catalyst was dried over a period of 8hours at 85° C. under 1.13 millibars.

Yellow pellets containing 0.44 wgt % Rh were obtained.

Catalyst No. 2

Al₂ O₃ ] [Rh(dpe)₂ ]⁺ BF₄ ⁻

3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameter of3 mm, an inner BET-surface area of 125 m² /g and a pore volume of 0.9ml/g were added to 100 mg (10.4 mg Rh) compound of the formula [Rh(dpe)₂]BF₄ (melting point=270° C.; prepared the same way as catalyst No. 1 butwith an additional anion exchange with AgBF₄ for increasing theperformance; cf. B. R. James et al., Can. J. Chem. 57, 180 (1979))dissolved in 100 ml dichloromethane under N₂. The yellow suspension washeated to boiling while stirring, refluxed over a period of 12 hoursafter which the dichloromethane was found to have been completelydecolorized. Next, the dichloromethane was removed under reducedpressure and the catalyst was dried for 8 hours at 85° C. under 1.13millibars.

Yellow pellets containing 0.32 wgt % Rh were obtained.

Catalyst No. 3

SiO₂ ] [Rh(dpe)₂ ]⁺ BF₄ ⁻

4 g activated silicon dioxide (98% SiO₂) which had a diameter of 3 mm,an inner BET-surface area of 280 m² /g and a pore volume of 0.95 ml/gwas added to 193 mg (20.1 mg Rh) compound of the formula [Rh(dpe)₂ ]BF₄dissolved in 100 ml dichloromethane under N₂. The yellow suspension washeated to boiling while stirring and refluxed over a period of 12 hoursafter which the dichloromethane was found to have been completelydecolorized. Next, the dichloromethane was removed under reducedpressure and the catalyst was dried for 8 hours at 85° C. under 1.13millibars.

Yellow pellets containing 0.47 wgt % Rh were obtained.

Catalyst No. 4

Al₂ O₃ ] [Rh(dpb)(CO)Cl]₂

5.3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameterof 3 mm, an inner BET-surface area of 125 m² /g and a pore volume of 0.9ml/g were added to 29 mg (5.04 mg Rh) compound of the formula[Rh(dpe)(CO)Cl]₂ (melting point=182° C.; prepared from1,4-bis-(diphenylphosphine)butane and dichlorotetracarbonyldirhodium;cf. A. R. Sanger, J. Chem. Soc. Dalton Trans (1977), 120) dissolved in50 ml dichloromethane, under N₂. The yellow suspension was heated toboiling while stirring and refluxed over a period of 18 hours afterwhich the dichloromethane solvent was found to have been completelydecolorized. Next, the dichloromethane was removed under reducedpressure and the catalyst was dried for 8 hours at 85° C. under 1.13millibars.

Yellow pellets containing 0.08 wgt % Rh were obtained.

Catalyst No. 5 ##STR3##

6.3 g activated chromium/aluminum oxide cylinders (5.29 g Al₂ O₃ +1.01 gCr₂ O₃) with the dimensions of 4×4 mm and with an inner BET-surface areaof 68 m² /g were added to 200 mg (20.9 mg Rh) compound of the formula[Rh(dpe)₂ ]BF₄ dissolved in 100 ml dichloromethane, under N₂. The greensuspension was heated to boiling while stirring and refluxed over aperiod of 24 hours after which the dichloromethane was found to havebeen completely decolorized. Next, the dichloromethane was removed underreduced pressure and the catalyst was dried for 8 hours at 85° C. under1.13 millibars. Green pellets containing 0.3 wgt % Rh were obtained.

Catalyst No. 6

Al₂ O₃ ] [Rh(tetraphos I)]⁺ PF₆ ⁻

3.5 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameterof 3 mm, an inner BET-surface area of 125 m² /g and a pore volume of 0.9ml/g were added to 100 ml (11 mg Rh) compound of the formula[Rh(tetraphos-I)]⁺ PF₆ ⁻ (melting point=314° C.; prepared from (Pφ₃)₃RhCl and tetraphos-I; cf. R. B. King et al., Inorg. Chem. Vol. 10(1971), page 1851 et seq) dissolved in 50 ml dichloromethane, under N₂.The yellow suspension was heated to boiling while stirring and refluxedover a period of 16 hours after which the dichloromethane was found tohave been completely decolorized. Next, the dichloromethane was removedunder reduced pressure and the catalyst was dried for 8 hours at 85° C.under 1.13 millibars.

Yellow pellets containing 0.3 wgt % Rh were obtained

Catalyst No. 7 ##STR4##

3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameter of3 mm, an inner BET-surface area of 125 m² /g and a pore volume of 0.9ml/g were added to 100 mg (10.4 mg Rh) compound of the formula [Rh(dpe)₂]BF₄ and 100 mg (9.25 mg Cr) compound of the formula [Cr(dpe)(CO)₄ ](prepared as described by J. Chatt et al., J. Chem. Soc. (London) 1961,pages 4980 et seq.) dissolved in 100 ml dichloromethane, under N₂. Theyellow suspension was heated to boiling while stirring and refluxed overa period of 12 hours after which the dichloromethane was found to havebeen completely decolorized. Next, the dichloromethane was removed underreduced pressure and the catalyst was dried for 8 hours at 85° C. under1.13 millibars. Yellow pellets containing 0.31 wgt % Rh and 0.28 wgt %Cr were obtained.

Catalyst No. 8 ##STR5##

0.1 g sodium iodide dissolved in 30 ml acetone was added while stirringto 3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameterof 3 mm, an inner BET-surface arae of 125 m² /g and a pore volume of 0.9ml/g, and the whole was heated to boiling, and refluxed over a period of48 hours. Next, the solvent was removed and the catalyst balls weredried for 8 hours at 85° C. under 1.13 millibars.

The rhodium was applied as described hereinabove for catalyst No. 2

Yellow pellets containing 0.31 wgt % Rh and 3.12 wgt % NaI wereobtained.

Catalyst No. 9

Al₂ O₃ ] [Rh(dpen)₂ ]⊕ClO₄ ⊖

100 mg (10.3 mg Rh) compound of the formula [Rh(dpen)₂ ]⊕ ClO₄ ⊖(prepared as described by W. A. Fordyce et al., Inorg. Chem. 1982, 21,pages 1455-61) dissolved in 100 ml dichloromethane was added under N₂ to3 g activated aluminum oxide balls (99% Al₂ O₃) which had a diameter of3 mm, an inner BET-surface area of 125 m² /g and a pore volume of 0.9ml/g. The light yellow suspension was heated to boiling and refluxedover a period of 12 hours after which the solvent was found to have beencompletely decolorized. Next, the solvent was removed under reducedpressure and the catalyst was dried for 8 hours at 85° C. under 1.13millibars. Yellowish pellets containing 0.33 wgt % Rh were obtained.

We claim:
 1. In the process for making monocarboxylic anhydrides of theformula (RCO)₂ O by reacting a carboxylic acid ester or dialkylether ofthe formulae RCOOR and ROR, respectively, in which R stands for one andthe same alkyl radical having from 1-4 carbon atoms, with carbonmonoxide in gas phase, in the presence of iodine or bromine or theircompounds as a reaction promoter and also in the presence of acarrier-supported catalyst containing noble metal compounds belonging togroup VIII of the Periodic System, at temperatures of 130°-400° C. andunder pressures of 1-150 bars, the improvement which comprises: using acarrier-supported catalyst in which the carrier material has a noblemetal/chelate-compound formed of the noble metal compound and a chelatorcontaining organonitrogen, organophosphorus, organoarsenic ororganosulfur groups applied to it, the chelator being selected from thegroup consisting of(a) Y--(CH₂)_(n) --Y (b) Y--CH═CH--Y (c) φ₂P--CH═CH--Pφ₂ (d) φ₂ As--CH═CH--Asφ₂ (e) φ₂ P--CH₂ --CH₂ --Pφ--CH₂ --CH₂--Pφ--CH₂ --CH₂ --Pφ₂ (f) φ₂ P--CH₂ --CH₂ --Pφ--CH₂ --CH₂ --Pφ₂ ##STR6##(h) P(--CH₂ CH₂ Pφ₂)₃ (i) R¹ --C[--(CH₂)_(n) --Y]₃ ##STR7## in which φstands for C₆ H₅ --;Y stands for --NR₂ ², an aryl group containingnitrogen, --PR₂ ², --AsR₂ ², --SR² or SH; R¹ stands for --H, a C₁ -C₅-alkyl or --C₆ H₅ ; R² stands for a C₁ -C₆ -alkyl, a C₅ -C₈ -cycloalkylor --C₆ H₅ or C₆ H₅ CH₂ --; n stands for 1 through 6; m stands for 0through 8, and x stands for 1 or
 2. 2. A process as claimed in claim 1,wherein the carrier material of the carrier-supported catalyst has a nonnoble metal/chelate compound formed of a non noble metal compoundselected from the 6th or 8th subgroup of the Periodic System of theelements and the chelator as an additional constituent applied to it. 3.A process as claimed in claim 1, wherein the carrier-supported catalystcontains a non noble metal compound selected from the 1st through 3rdprincipal groups or the 4th through 6th or 8th subgroups of the PeriodicSystem of the elements as an additional promoter.
 4. A process asclaimed in claim 1, wherein R² stands for a C₁ -C₆ alkyl, a C₅ -C₈-cycloalkyl or --C₆ H₅ or C₆ H₅ CH₂ -substituted with halogen, methoxy,ethoxy or a C₁ -C₃ -alkyl.
 5. A process as claimed in claim 1, whereinthe carrier-supported catalyst contains an inorganic oxidic carrier oran active carbon carrier.
 6. A process as claimed in claim 1, whereinthe carrier-supported catalyst contains 0.01-50 wgt % chelate compound.7. A process as claimed in claim 1, wherein the carrier-supportedcatalyst contains altogether 0.01-50 wgt % chelate compound and nonnoble metal compound.
 8. A process as claimed in claim 1, wherein thecarrier-supported catalyst is used in the form of particles having asize of 1 through 20 mm.